Thank you for joining the Intel® NUC community. I am sorry to hear you are having issues with the audio on this unit.

Have you tried reinstalling all the proper drivers for your Intel® NUC and this operating system? I would recommend this before considering this matter as a hardware failure. From my end, the support for Linux is limited; therefore, my recommendation is to use Ubuntu forums in order to get check if your system is up to date, visit the community here: Ubuntu Forums. One more thing I would recommend in your case is to test Ubuntu 16.04.

Regarding your question, in case you are able to confirm a hardware failure the whole unit would need to be replaced.